Fan construction



W. A. OMOHUNDRO May 28, 1968 FAN CONSTRUCTION 2 Sheets-Sheet 1 FiledMarch 31, 1966 m QM %B M May 28, 1968 A. OMOHUNDRO 6 FAN CONSTRUCTIONFiled March 51, 1966 2 Sheets-Sheet 2 m mq Z:

United States Patent Ofice 3,385,516 FAN CONSTRUCTIGN William A.Omohundro, Westport, onn., assignor to General Electric Company, acorporation of New York Filed Mar. 31, 1966, Ser. No. 539,055 6 Claims.(Qi. 23tl-259) ABSTRACT 9F THE DISCLOSURE A reversible electric fanhaving a fan blade and hub construction molded from a plasticcomposition which softens and hence may deform at temperatures onlyslightly higher than normal operating range. Cooling passages are formedin the hub to direct cooling air over the plastic hub parts even withair flow blocked and upon either direction of rotation.

This invention relates to electric fans and more particularly to animproved fan blade and hub construction.

While the invention described herein is not limited to a particular sizefan, it is particularly useful and advantageous in connection with theso-called twenty inch fans which are manufactured in large volume andprimarily sold to individuals for use in private dwellings. In view ofthe highly competitive nature of this business, it is extremelyimportant that the fan be constructed as inexpensively as possible whileyet providing the efficiency and reliability required. An improvement injust one component frequently results in compounded savings. Forexample, if a fan blade can be made more compact and with less material,savings are not only realized from re duced material costs of the fanproper, but a smaller, lighter and less costly motor and fan casing maybe employed. This, in turn, results in reduced packaging andtransportation costs. Naturally, a lighter fan is also more convenientfor the consumer to handle.

Substantial weight reduction can be obtained by utilizing plastic orsimilar lightweight materials for the fan blade as opposed to usingmetal such as steel. On difficulty encountered in using fan blades madeof low cost plastic material is that the material is not sufiicientlystrong and heat resistant to withstand abnormal operating situations towhich it may be subjected by the user. For

example, the twenty inch fan is most often positioned adjacent a windowframe for operation, and it is not uncommon for a user to inadvertentlyenergize the motor when the window is closed. This obstruction to theair flow will cause the motor to be overloaded, with a resulting heatrise. Unless special provision is made to protect the fan blade fromsuch heat, a blade of low cost plastic will distort and fail. It istherefore desirable that the plastic blade be able to satisfactorilywithstand such abnormal condition.

In view of the foregoing, it is a primary object of this invention toprovide a fan having an improved low cost plastic blade constructionwhich can withstand the extra heat generated by the fan motor when theair flow of the fan is obstructed.

It is another object of this invention to provide an improved low costplastic fan blade which restricts the heat flow from the fan motor tothe blade and has provision in its hub portion for permitting air flowtherethrough.

It is a further object of this invention to provide an improved low costelectric fan having a light weight plastic blade construction which hasa minimum of axial depth and a high air output.

In accordance with one aspect of this invention, there is provided a fanblade made of plastic which will deform when subjected to normal fanoperating forces at temperatures somewhat above normal operation. The

3,385,515 ?atented May 28, 1968 blade is provided with a plurality ofblade elements extending outwardly from a central hub and is rotated bya motor drivingly connected to the hub and partially position within thehub. The hub is formed with a series of air passages for permitting airflow through the hub to prevent a heat build up by the motor which wouldcause the plastic blade to soften and fail and possibly cause motorfailure. With such construction, plastic materials may be employed forthe fan blade, thus providing a low cost unit which is also lighter andhence easier for the user to handle.

To obtain a given air flow with a plastic fan blade, it has been foundthat five blade elements is the optimum in that the axial depth of theelements can be made smaller than when using fewer elements. Smallerelements, of course, require less plastic to retain their shape, hencelower cost and lighter weight. Also, with the reduced axial depth, ashallower casing can be used to enclose the unit resulting in furthersavings in weight and cost.

Further features, objects and advantages will become apparent withreference to the following written description and drawing in which:

FIG. 1 is a perspective view of a portable twenty inch electric fan;

FIG. 2 is a front elevation-a1, partially cut-away view of the fan;

FIG. 3 is a rear perspective view of the blade hub of FIG. 2;

FIG. 4 is a crosssectional view of the fan blade along the line of 4-4of FIG. 3 and including a side view of a portion of the motor;

FIG. 5 is a schematic view of a fan in operation during closed windowsituation;

FIG. 6 shows the fan of FIG. 5 operating in the reverse direction;

FIG. 7 is a front elevational, partially cutaway view of an electric fanhaving a modified form of fan biade hub; and

FIG. 8 is a partial cross-sectional view taken substantially along theline 8-8 of FIG. 7.

Referring now to the drawings, there is shown in FIG. 1 a twenty inchelectrical household fan having an external rectangular casing 10, agrille 12, an orifice plate 14, a fan blade 16 driven by a motor 18, anda switch 20 for controlling energization of the motor. The fan blade 16includes a central somewhat cup-shaped or cylindrical hub 22 and fiveblade elements 17 formed integrally wth the hub and extending radiallyoutwardly therefrom.

In accordance with the invention, it is desirable that the fan blade 16be formed of plastic or other similar lightweight material so that theblade can be molded as a one-piece integral unit. While various plasticmaterials may be employed, good results with reasonable cost have beenobtained from a plastic known as acrylonitrile butadiene styrene,commonly referred to as ABS. Although such material has many desirablecharacteristics, one of its disadvantages is that when used in a fanblade, it can only withstand temperatures on the order of 180 F. beforeit will become somewhat distorted while under the stresses of fanoperation. Another suitable material is polypropylene which while not asstrong as ABS at low temperatures, can withstand fan stresses betterthan ABS at temperatures on the order of 270 F.

It has been found that during normal operating conditions a fan blademade of either of the above-mentioned low cost plastics can adequatelywithstand the heat generated by the motor when subjected to normaloperating stresses. However, a commercially successful fan should beable to satisfy safety and performance requirements even under anabnormal operating condition if such condition is likely to occur.

As mentioned above, quite often fan users operate a twenty inch fan neara window and the fan is occasionally inadvertently energized while thewindow is closed. Under such conditions, the air fiow generated by thefan is naturally severely restricted and the motor is overloaded causingincreased heat generation. It has been found that unless this heat isdissipated, the temperature to which the plastic blade is subjected isquickly raised above 300 F. Such temperature will rapidly distort lowcost plastics of the type previously mentioned, particularly when underoperational stresses.

In accordance with the invention, to overcome this problem and to makethe use of low cost plastics possible, air passages have been formed inone end of the hub 22. It has been found that when a fan withoutpassages in the hub is operating adjacent a closed window, a largepressure differential is built up between the front and back of the fan,With no release, this causes the motor to heat; and with the restrictedair movement, the heat is not dissipated. By introducing air passages,the air has an escape and the resulting air movement through the hub inand over the motor cools these components. The result is that theplastic hub does not reach its distortion point and does not fail.

Incidentally, it should be noted that the direction of air flow throughthe hub in the closed window situation is dependent on the direction thefan is rotating. When the fan is directing air toward the closed window23 as shown schematically in FIG. 5, air is forced through the hubapertures and in and around the motor. When air is directed by the fanaway from the closed window as in FIG. 6, air is drawn over the motorand through the hub apertures.

With certain plastics, the entire fan blade including the air movingelements and the hub may be formed as a single plastic unit. However, tofurther improve the heat withstanding characteristics of thearrangement, a metal insert may be positioned within one end of the hubto contact the motor shaft. The insert dissipates the heat from themotor shaft so that the temperature at the insert and plastic interfacedoes not rise to a level to cause distortion of the plastic. As can beseen from the drawings, and particularly FIG. 4, an insert 24 has beenutilized in the arrangement shown. The insert 24 may be connected to thehub in any suitable fashion.

With regard to the closed window situation, the particular shape of theair passages in the hub is not critical. However, it is also desirablethat some cooling effect for the blade be provided during normaloperation.

The fan element of the invention as shown in FIGS. 24, includes an innerannular series of alternately spaced passages 26 and solid sections 28within the insert. Since each of the passages 26 and solid sections 28within the inner annular series are substantially identical, only someare indicated by numerals in FIGS. 2 and 3 to simplify the appearance ofthe drawing. Considering the insert 24 in greater detail, it can be seenthat there is included a cylindrical shaft receiving portion 30 adaptedto fit over shaft 32 of motor 18. The insert may be secured to the shaft32 by a suitable set screw threaded into radially extending opening 34formed in the cylindrical portion 30 and one sector of the insert. Inthis connection, it should be noted that the insert has somewhat of afrusto-conical cross-section on one end thereof, as can be seen in FIG.4. Thus the opening 34 is easily accessible with a screw driver throughentry to one of the passages 26.

The insert further includes an annular wall 36 concentrically spacedfrom the inner cylindrical portion 30 and connected thereto by aplurality of radially extending walls 38. The solid sections 28 extendbetween alternate pairs of the radial walls 38. As can be seen fromFIGS. 2 and 3, each of the solid sections 28 has the shape of a sectionof a circle having its inner tip or apex removed; or in other words, itmay be said to have the shape of a truncated sector.

The air passages 26 also have a cross-section with the shape of atruncated sector when viewed from the air inlet side of the insert, asin FIG. 2. The entry to each of the passages is defined by a pair of theradial walls 38 and by the annular wall 36 and the outer wall of thecylindrical portion 30. With such an arrangement, the air during normaloperation enters the air passages 26 in substantially an axialdirection. However, each of the passages 26 is further provided with acurved wall or vane 40 which slopes rearwardly and radially outwardlyfrom the righthand end or front of the insert as viewed in FIG. 4. Thecurved walls or vanes 40 cause the series of passages to serve as aminiature centrifugal type fan in that the air is drawn in through theright end of the passages, as viewed in FIG. 4, and is directed in acombined xially and radially outward manner. It should be noted thatduring normal operation the air flows through the insert passages inthis fashion regardless of which direction the fan blade is rotated.

To improve the structural strength of the assembly, there is provided aplurality of radially extending ribs 42 which connect the radially innersurface of vanes 40 to the inner cylindrical section 30. It should beunderstood that the insert is actually a skeletonized structure in thatit is basically hollow except for the ribs and walls which have beenmentioned. Such a unique arrangement requires a minimum amount ofmaterial but yet provides the necessary structural strength. Moreoverthe walls and ribs have been so designed that the insert can be easilymolded.

Turning now to the remainder of the hub construction, an annular wall 44surrounds Wall 36 of the insert 24. These two walls may be formed as asingle wall if the entire hub is molded as one piece. Another annularwall 46, which has an axial dimension greater than that of the axialdimension of wall 44, is concentrically spaced from wall 44. A pluralityof radially extending walls 48 are e uall s aced wnnm tne annularsection defined by walls 44 and 46. These walls 48 have an axialdimension approximately equal to that of wall 44 and are radiallyaligned with walls 38 within the insert 24.

A plurality of solid sections 50 extend between alternate pairs of walls48 and between annular walls 44 and 46. Surrounding these solid sections50 and the right end of wall 46, as viewed in FIG. 4, is an annular wall52, which is, in turn, connected to cylindrical portion 54 of the hub.Between each pair of solid sections 50 there is formed an air inletdefined by alternate pairs of walls 48 and by the right end of annularwall 44 and the inner edge of annular wall 52. These inlets mark theentry to a plurality of air passages 58 defined by alternate pairs ofwalls 48 and by a plurality of curved walls or vanes 60. As can be seenfrom FIG. 4, the vanes 60 extend from the right or outer end of wall 44to a point on wall 46 which is approximately radially aligned with theleft end of wall 44. The portions of the vanes 60 which combine withwall 46 define air outlets 62 from air passages 58 together withalternate pairs of walls 48 and with the inner edge of wall 52; or inother words, there is formed a plurality of air outlets 62 in annularwall 46 at locations which are equally spaced around the hub betweenalternate pairs of walls 48. a

Outlets 62 lead into hollow areas or passages 59 defined by the axiallyinner face of wall 52, by the radial inner surface of cylindricalportion 54 and by alternate pairs of radially extending walls 64 whichextend between wall 46 and cylindrical portion 54. As can be seen inFIG. 4, the walls 64 taper axially toward the left end of cylindricalportion 54 to provide structural strength to the hub. From FIG. 3 it canbe seen that radial walls 64 are radially aligned with wall 48 and 38.As can be seen by the arrows in FIG. 4, the air passages 58 and 59function to draw air through the hub and around the motor 18 by acentrifugal fan action in approximately the same manner as the airpassages within the insert 24. Thus, the air enters in an axialdirection and is ducted axially and radially outwardly through passages53 before being once more directed axially by the walls of passages Toprovide additional structural strength to the hub, there is formed aseries of radially extending ribs 66 integrally formed with the back ormotor side of sections 50 and extending between walls 44 and 45, as seenin FIG. 3. Similarly, on the back or motor side of vanes 6t) there isformed a series of radially extending ribs 58 which extend outwardlyfrom annular wall 44 and terminate slightly before reaching wall 46.

Now that the overall construction has been described in detail, theoperation of the hub and insert can be more easily appreciated. Bothseries of air passages 26 and S3, 59 serve as centrifugal air movingdevices during normal operation which draw air through the hub to coolthe plastic blade. The inner series of passages 26 are primarilydesigned to cool the inner section of the hub, whereas the other seriesof passages 58 are primarily de signed to cool the outer portions of thehub. The auxiliary fins 74 formed integral with the rotor also cause aircirculation to cool the adjacent components. Motor cooling is alsoprovided by the series of ribs 64 as they circulate air around themotor.

Note that the inner series of passages 26 are circumferentially off-setfrom the outer series of passages; or in other words, each inner passage26 is radially aligned with an outer solid section 50, and each innersolid section 28 is radially aligned with an outer air passage 58. Suchan arrangement provides uniform air distribution and at the same timecontributes to the overall strength of the construction. It should alsobe noted that although there are a considerable number of differentwalls and ribs employed in the design, they are positioned so as tofacilitate a molding operation, and to provide maximum strength with aminimum of material.

As has been mentioned, the entire fan blade and hub construction can bemade as a single integral unit or if the materials employed cannotwithstand abnormal heat conditions, the central portion of the hub maybe formed as a separate insert. The primary purpose of the insert is ofcourse to prevent excessive heat from reaching the more easily deformedplastic material of which the remainder of the blade is formed. However,this can be accomplished in more than one way. By making the insert of amaterial which is a good heat conductor, such as most metals, andproviding the insert with air cooling passages, heat from the motor canbe dissipated to the air so that the temperature of the hub portionssurrounding the insert is kept below a desired level. Also, due to thelarger diameter of the insert, the heat density of the outer surface ofthe insert is reduced from that of the shaft.

Alternatively, the insert may be formed of a material which is a poorheat conductor, with the idea being that the heat from the motortransmitted through the shaft is blocked by the insert from beingconducted to the surrounding hub. In effect, the heat is confined to themotor and its shaft. By the use of the cooling air passages, this heatmay be removed from the motor to keep its temperature below a desiredlevel.

As explained, the hub construction described permits the use oflightweight, low cost plastics for fabricating the blade. This advantageis maximized when a minimum amount of material is employed. Inaccordance with the present invention, the blade is provided with fiveindividual elements in that it has been found that this number ofelements requires the least amount of material for a given air output ofa twenty inch fan. Some of the reasons for this are that with fiveelements, each individual blade moves less air and is under less stressthan each element in a blade having a fewer number of elements so thatthe thickness of each element can be minimized. In the present instance,excellent results have been obtained by tapering the element thicknessfrom .10 inch at the end of the element connected to the hub to .05 inchat its outer tip.

With such relatively thin plastic blade elements, it is very importantthat the stresses on the elements be minimized. When a blade is rotated,the centrifugal forces produced are radially directed on linesperpendicular to the rotational axis. Hence, it is desirable that theblade elements be formed with the surfaces aligned with these expectedcentrifugal forces. To obtain efficient fan operation, it is alsodesirable that the blade element surfaces be twisted rather than planar.In accordance with the invention, a preferred shape is the so-calledhelical blade element which is generated by a radial line perpendicularto the rotational axis moving on the hub surface in a slightly curvedpath. Such a blade element shape is aligned with the centrifugal forces.

Further, when utilizing five blades as opposed to a lesser number ofblades, the pitch or axial dimension of the blade is less, so that thehub is axially shorter and the individual elements are axially shorter,thus further reducing the amount of material required. In the twentyinch fan blade illustrated, the axial dimension of wall 58 is less thanthree inches. To further reduce the overall axial dimension of the fan,the rotor fins 74 are formed with outer edges curved to complement thecup-shape of the hub 22. This permits more of the motor to fit withinthe hub. This increased compactness also helps to reduce packing andshipping expenses.

Another advantage of utilizing a blade with a minimum of axial depth isthat it is particularly suited for use with an electrically reversiblefan in that the orifice plate 14 can be centrally positioned withrespect to the blade and substantially the same output can be obtainedfrom the fan when rotated in either direction. Utilizing more than fiveblade elements in a blade of the type herein described decreasesefficiency to an undesirable level and also increases noise problems.Thus from an overall viewpoint, outstanding performance is obtained witha five element blade having the characteristics described.

To further reduce the amount of plastic required to fabricate the hub,the rear section of hub cylindrical portion 54 has a recess 76 formedbetween each pair of elements 17. The full axial dimension of the recess76 is shown in FIG. 4; and note that the recess does not extend quite tothe right edge of stator plates 70. With such an arrangement the thinplastic blade surface adjacent recess 76 is not exposed to the statorcoils 72. This is a safety requirement of Underwriters Laboratories forplastic blade elements in that if the plastic used for the blade is notself-extinguishing, the material must be protected. One method is withfire preventing paint. The paint must be applied where there islikelihood of flame contacting plastic. Therefore, the present designsurrounds coils with a circular flange where the paint is applied;otherwise the entire fan blade might require this paint.

Referring now to FIGS. 7 and 8 which illustrate a modified fanconstruction embodying features of the present invention, there is showna fan blade generally designated 7 3 having a cup-shaped hub 80 and fiveblade elements 82 integrally molded from a resin plastic material. Thehub 80 has a circular end portion 84, a cylindrical skirt portion 86having the blade elements 82 extending from the outer surface thereof,and an annular portion 83 positioned centrally of the end portion andconcentrally of the skirt portion. The hub. 80 is also provided with amolded-in place metal insert which is partially enclosed by the annularportion 88 and is rigidly secured thereto against either axial orrotational movement in any suitable manner as will be readily apparentto those skilled in the art. The insert 90 is adapted to slidingly fitover shaft 92 of electric motor 94 and has an end positioned outwardlyfrom the hub end portion 84 provided with a set screw 96 to secure theinsert, and thereby the fan blade 78, to the motor shaft.

In order to prevent deterioration of the plastic fan blade 78 as aresult of overheat conditions during the abnormal operating conditionshereinbefore described, the

hub 80 is provided with a series of circumferentially spaced apertures98 extending through the end portion 84 positioned radially above andadjacent to the radial outer surface of the annular portion 88. Theapertures 98 communicate with a series of air flow passages 100 formedinternally of the hub 80 and defined by the side surfaces of radiallyextending walls or vanes 102, the inwardly facing surfaces of the hubend portion 84 and skirt portion 86, and the radial outer surface of theannular portion 88. The number of vanes 102 may correspond to the numberof apertures 98 so that each aperture communicates with a single airpassage 100. Such an arrangement imparts high structural rigidity to thehub 80. It is to be understood, however, that a lesser number of vanes102 would be acceptable when the fan blade 78 is made from a plasticmaterial having the necessary strength and rigidity characteristics; forexample, two adjacent apertures 98 may communicate with a single airpassage 100, in which case the number of vanes 102 would be one-half thenumber of apertures 98, whereby the amount of plastic material requiredto form the blade may be correspondingly reduced.

The vanes 1102 have a lower portion extending radially upwardly from thehub annular portion 88 and curving in the direction towards the motor 94to merge with an upper portion extending substantially the full lengthof the hub skirt portion 86 and tapering outwardly and in the directionof the motor, as best seen in FIG. 8. With this vane construction, thepassages 100 function during operation of the fan as a centrifugalblower. In normal operation, air is drawn in through the apertures 98and directed in a combined axial and radially outwardly path asindicated by the arrows in FIG, 8. The various parts of the plastic hub80 and adjacent surfaces of the motor 94 are thus subjected to currentsof cooling air and the plastic of the fan blade is thereby maintained atan acceptably low temperature. It should be noted that theaforementioned centrifugal blower effect and cooling air flow occursduring normal operation of the fan irrespective of the direction inwhich the fan blade 78 is being rotated.

When the air flow generated by the fan is severely restricted as in theclosed window situation, the apertures 98 permit cooling air to flowthrough the hub 80 in the manner shown in FIGS. 5 and 6, depending uponthe direction of rotation of the fan blade. As previously described,restriction of the fan output causes the motor to become overloaded andconsequently to overheat. Moreover, this overheat condition isaggravated by the fact that the cooling air flow over the motor isitself reduced. By providing the apertures 98 which result in a coolingair fiow through the hub 80 and over the motor 94 because of the largepressure difierential existing between the two sides of the fan blade 78in the restricted flow condition, the plastic hub components areprevented from becoming heated to the temperature at which the materialwould soften and thereby result in distortion and failure of the fanblade.

Other modifications and variations of the present invention are possiblein the light of the above teachings. It is, therefore, to be understoodthat all such variations and modifications within the spirit and scopeof the invention are intended to be included within the appended claims.

What is claimed is:

1. In a fan construction, a fan blade made of plastic which will deformunder fan operating forces at temperatures slightly above the normaloperating range; said blade having a plurality of elements extendingoutwardly from a central hub; a reversible motor having a shaft fordrivingly receiving said hub; said hub having a series of air passagesfor directing cooling air flow through the hub to prevent thetemperature of the hub from rising to a level to deform the hub duringabnormal fan operation wherein the air flow of the fan is substantiallyobstructed in either direction of rotation.

2. The fan construction of claim 1 in which a metal insert is positionedin the central portion of said hub to engage said shaft, said airpassages being formed in said insert.

3. The fan construction of claim 1 wherein said hub is formed with aseries of inwardly extending, axially oriented vanes for circulating airadjacent said motor to provide motor cooling.

4. The invention of claim 1 in which said blade elements have a helicalshape so that centrifugal forces produced by rotation of the blade donot tend to change the shape of the blade elements.

5. In a fan construction, a plastic fan blade having a plurality ofblade elements extending radially outwardly from a central hub; anannular series of alternately spaced openings and solid sections withinone end of said hub facing generally an axial direction; a metal insertcentrally positioned within and secured to said hub end; said inserthaving an annular series of alternately spaced openings and solidsections radially inwardly positioned from said series within said hubfor directing cooling air through insert; said insert series and saidhub series being circumferentially arranged with respect to each otherso that a solid section within the insert series is radially alignedwith an opening in the hub series and an opening in the insert isaligned with a solid section in said hub series.

6. In a fan construction, a plastic fan blade having a generallycup-shaped hub and a plurality of blade elements extending radiallyoutwardly from the side walls of the hub; an electric motor adapted tofit partially within said hub and having an output shaft; a metal insertcentrally positioned within and secured to one end of said 1111b; saidinsert having a central opening adapted to be secured to said motorshaft; said insert having an annular series of spaced air passages forpermitting air flow through the insert to disperse heat from said motorand thus prevent the temperature of said plastic hub from reaching alevel where it would deform, said hub having an annular series of spacedair passages surrounding said insert.

References Cited UNITED STATES PATENTS 2,303,832 12/1942 Funk 230l34.22,307,283 1/1943 Lonergan 230117 2,620,970 12/1952 Palmer et a1 230-2592,709,035 5/1955 Schmidt 23O259 2,870,959 l/1959 Giddings 230-1343,178,099 4/1965 Child 230134.2 3,303,995 2/1967 BOeekel 2302S9 DONLEYJ. STOCKING, Primary Examiner. LAURENCE V. EFNER, Examiner.

